1. Field of the Invention
The present invention relates to adaptive optics and, more specifically, to micro-electromechanical systems (MEMS) for implementing adaptive optics.
2. Description of the Related Art
Adaptive optics is a field of optics dedicated to the improvement of optical signals using information about signal distortions introduced by the environment in which the optical signals propagate. An excellent introductory text on the subject is given in “Principles of Adaptive Optics” by R. K. Tyson, Academic Press, San Diego, 1991, the teachings of which are incorporated herein by reference.
A representative example of an adaptive optical element is a deformable mirror driven by a wavefront sensor and configured to compensate for atmospheric distortions that affect telescope images. Small naturally occurring variations in temperature (˜1° C.) in the atmosphere cause random turbulent motion of the air and give rise to changes in the atmospheric density and, hence, to the index of refraction. The cumulative effect of these changes along the beam propagation path may lead to beam wandering and spreading and to beam intensity fluctuations, each of which degrades image quality. The wavefront sensor is a device that measures the distortions introduced in the atmosphere and generates feedback for the deformable mirror. Based on the feedback, the mirror is deformed such that the beam distortions are significantly reduced, thus improving the image quality.
U.S. Pat. No. 6,384,952, the teachings of which are incorporated herein by reference, discloses a representative prior-art device having a deformable membrane mirror connected to a plurality of actuators. To enable the membrane deformations, each actuator has two interleaved comb-shaped portions connected between the membrane and a substrate and offset with respect to each other in the direction perpendicular to the substrate. During the device fabrication process, the offset comb-shaped portions are typically formed in different layers of a layered wafer, which may result in certain wafer processing problems. For example, it may be relatively difficult to achieve proper alignment of the interleaved structures of said comb-shaped portions with respect to each other because different layers are processed during different fabrication steps using different lithographic masks.